Re: Thread safety problems with function scope static variables vs
class static private members
On Dec 19, 12:49 pm, Juha Nieminen <nos...@thanks.invalid> wrote:
James Kanze wrote:
On Dec 18, 6:41 pm, "Hicham Mouline" <hic...@mouline.org> wrote:
void C::f() {
static const int keys[] = { 0, ...., 15 };
}
No. In both cases, you have static initialization, which is
guaranteed to occur before anything else.
I thought that a static inside a function is initialized the
first time the function is called?
The standard explicitly says otherwise: "Objects of POD types
with static storage duration initialized with constant
expressions shall be initialized before any dynamic
initialization takes place." (=A73.6.2/1).
In fact, in this case, the word static means what it says; such
variables are initialized statically, not dynamically.
The above function might not be problematic with regard to
thread safety, but what about something like this:
void foo()
{
static SomeClass object;
...
}
It depends on SomeClass, obviously. Does SomeClass use static
or dynamic initialization?
Suppose that 'foo()' may be called from more than one thread.
Can it happen that 'object' is constructed more than once?
Probably. I don't know what the next version of the standard
will say about it, but in current implementations, it's
undefined behavior to enter such a function from several
different threads without some sort of external synchronization.
But what does this have to do with static initialization?
--
James Kanze (GABI Software) email:james.kanze@gmail.com
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